The purpose of this Mentored Research Scientist Development Award (K01) is to provide the candidate with the training and expertise needed to transition to research independence in the science of HIV/STI prevention and intervention. The candidate plans to assess how substance use and the epidemiology of HIV/STI are shaped by physical and social contexts, using this information to design high-impact interventions. To achieve these goals, the proposed career development plan has been designed to augment the candidate's current training in sociology and epidemiology and enable her to: 1) build expertise on the evaluation of HIV/STI risk venues for high-risk females who inject drugs (PWID); 2) develop methodological expertise in social network analysis, with a particular focus on two-mode network methods; 3) gain conceptual and methodological skills in the design of structural interventions focused on venues and risk networks; and 4) obtain additional training in the ethical conduct of place-based, network, and intervention research. These training goals will be achieved through a combination of didactic courses, specialized workshops, hands-on research, and mentoring from an interdisciplinary team of experts. Despite a low national HIV prevalence, incidence is rising among vulnerable populations along the US-Mxico border, especially high risk females. In Tijuana, HIV sequencing data indicates that the local epidemic is characterized by multiple new viral introductions, bridging across risk groups, and phylogenetic clustering among women. This suggests that interventions with high risk women could reduce HIV/STI incidence by tapping into their connections to other high risk groups. Using field observations and survey data on venue affiliations, the proposed research will assess underlying HIV/STI transmission dynamics by identifying venues where high risk networks converge (e.g. bars, shooting galleries, street intersections) and examining how the physical features of these venues (e.g. type, location, policies, safety) and affiliation network patterns (i.e. people's connections to these places) drive substance use, HIV/STI risk behaviors and infection. Incorporating detailed venue information into two-mode network analysis involving high risk female PWID will enhance research on local pathogen transmission patterns and inform targeted public health efforts aimed at reducing HIV/STI incidence. Additionally, the data collected as part of this K01 will inform the development of venue/network-level structural intervention strategies for high risk female PWID. This research responds to the FY2016 Trans-NIH Plan from the Office of AIDS Research, which calls for research on how best to target HIV prevention and treatment resources.114 The proposed research will be conducted as an independent adjunct to an existing NIH/NIDA-funded study that assesses criminal justice and HIV among PWID (R37DA019829, PI: Strathdee), capitalizing on its infrastructure and team of experts. The research findings and methodological skills to be gained from this K01 have wide applicability for infectious disease research and high transferability across diverse research settings.